Heretofore, where a workpiece is ground with a grinding wheel, it has been a practice that coolant for cooling and lubrication is supplied to a grinding point between the workpiece and the grinding wheel to prevent grinding burn, heat stress or the like from being generated on the workpiece by the cause of grinding heat.
Recently, a coolant supply method as described in Japanese unexamined, published patent application No. 2004-17265 has been developed for performing sufficient cooling and lubrication of a workpiece and a grinding wheel in a small quantity of coolant. In the coolant supply method described in the patent document, as shown in FIG. 6 of the patent document, at the same time as the supplying of coolant is started, an air jet is blown at a position behind or upstream of a grinding point in a grinding wheel rotational direction to traverse the grinding surface of the grinding wheel from one lateral side to the other lateral side. Thus, a wheel-following air layer which rotates to follow the grinding wheel is intercepted, so that a small quantity of coolant is well adhered to the grinding surface of the grinding wheel to be delivered reliably to the grinding point.
In grinding operation, a workpiece is ground by giving a grinding wheel a rough grinding feed and a finish grinding feed which are different in feed rate and is further ground in a spark-out state by temporarily discontinuing the grinding feed of the grinding wheel at the grinding feed end. During the grinding operation, heat generation increases with an increase in the infeed amount, and coolant of the flow quantity depending on the heat generation becomes necessary in order to cool down the heat generated by the grinding. For this reason, it is necessary to supply a large quantity of coolant during the rough grinding feed which is large in infeed depth and which thus causes heat to be generated to a high temperature.
By the way, in the coolant supply method described in the patent document, the supply of the air jet is started at the same time as the supply of the coolant is started, and the supply of the air jet is stopped at the same time as the supply of coolant is stopped. That is, the air jet is supplied throughout the grinding operation from start to end.
However, a large quantity of coolant is needed for cooling during the rough grinding operation, and when the air jet is supplied toward the grinding surface with the large quantity of coolant being supplied, it results that the large quantity of coolant is scattered to be suspended in the form of mist-within a cover device of the grinding machine. Thus, it is likely that the large quantity of coolant in the form of mist continues to be suspended within the cover device even after the completion of the grinding operation and flows out when the cove device is opened and closed for unloading and loading of workpieces, thereby to deteriorate the environment within the factory having the grinding machine installed. Further, where the inside pressure within the cover device of the grinding machine is heightened by the supply of the air jet, it is likely that the suspension of the large quantity of coolant causes a part of coolant to enter the inside of the grinding machine which ordinarily does not allow coolant to enter. This gives rise to a problem that the maintenance of the grinding machine has to be done at a high frequency.
The inventors of the present application carried out repetitive experiments for preventing the large quantity of mist-like coolant from being generated during the rough grinding feed and as a result, have found out that where supplied in a large quantity, coolant supplied reaches the grinding point by passing through a wheel-following air layer which rotates to follow the grinding wheel.